U.S. patent number 7,563,248 [Application Number 11/082,260] was granted by the patent office on 2009-07-21 for infusion fluid heat exchanger and cartridge.
This patent grant is currently assigned to Smisson-Cartledge Biomedical LLC. Invention is credited to Richard G. Cartledge, John M. Christensen, John M. Iaconis, Jeffrey W. Jerrell, Michael L. Koltz, Bradford J. Rainier, Hugh F. Smisson, III, Frederick J. York.
United States Patent |
7,563,248 |
Smisson, III , et
al. |
July 21, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
Infusion fluid heat exchanger and cartridge
Abstract
The present invention relates to a system for increasing the
temperature of a fluid being infused into a patient's body while
the infusion is taking place. The present invention also provides
for improved monitoring of air in the infusion system such to
prevent the introduction of air into the patient's body receiving
the fluid infusion. The present invention also provides for a
system pump which provides a variable flow rate that serves a vast
amount of infusion needs and purposes. A disposable cartridge in
accordance with the present invention will allow for the efficient
transfer of heat energy to the fluid being infused into the
patient's body. The cartridge will further ensure that deleterious
amounts of air will not be introduced into the patient's body.
Inventors: |
Smisson, III; Hugh F. (Macon,
GA), Cartledge; Richard G. (Hollywood, FL), Iaconis; John
M. (Monroeville, PA), Jerrell; Jeffrey W. (Greenfield,
WI), Christensen; John M. (Hamilton, OH), Koltz; Michael
L. (Ormond Beach, FL), York; Frederick J. (Longwood,
FL), Rainier; Bradford J. (DeLand, FL) |
Assignee: |
Smisson-Cartledge Biomedical
LLC (Macon, GA)
|
Family
ID: |
37011339 |
Appl.
No.: |
11/082,260 |
Filed: |
March 17, 2005 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060211988 A1 |
Sep 21, 2006 |
|
Current U.S.
Class: |
604/122;
604/113 |
Current CPC
Class: |
A61M
1/0281 (20130101); A61M 5/36 (20130101); A61M
5/44 (20130101); A61M 5/172 (20130101); A61M
5/16831 (20130101); A61M 5/365 (20130101); A61M
2205/127 (20130101); A61M 2206/10 (20130101); A61M
2206/14 (20130101) |
Current International
Class: |
A61F
7/12 (20060101); A61M 1/00 (20060101) |
Field of
Search: |
;604/31,65-67,113,122,131 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
US. Appl. No. 11/835,095, filed Aug. 7, 2007, Smisson, III et al.
cited by other .
U.S. Appl. No. 11/835,118, filed Aug. 7, 2007, Smisson, III et al.
cited by other .
U.S. Appl. No. 11/835,125, filed Aug. 7, 2007, Smisson, III et al.
cited by other .
U.S. Appl. No. 11/835,132, filed Aug. 7, 2007, Smisson, III et al.
cited by other.
|
Primary Examiner: Lucchesi; Nicholas D
Assistant Examiner: Eisenberg; Rebecca E
Attorney, Agent or Firm: Sutherland Asbill & Brennan
LLP
Claims
What is claimed is:
1. A disposable fluid infusion cartridge comprising a. a heat
exchanger comprising upper and lower aspects and an internal heat
exchange zone defined by a first and second plurality of
overlapping fins, creating a substantially uniform flow path depth,
wherein each fin has a ratio of height to width of at least 1:2,
whereby fluid enters the lower aspect of the heat exchanger via a
lower port and fills a lower flow cavity across the width of the
heat exchange zone prior to flowing at least partially across the
width of each succeeding overlapping fin and through the heat
exchange zone and out an upper port at the upper aspect of the heat
exchanger; and b. an air trap comprising upper and lower aspects
defining a longitudinal axis extending centrally therebetween, an
upper fluid input port, a lower fluid output port positioned
off-center from the longitudinal axis, an upper air output port,
and a fluid flow disrupter positioned off-center from the
longitudinal axis and proximate the lower fluid output port,
wherein the fluid input port introduces fluid into the air trap
from the heat exchanger in a circular flow, and wherein the
circular flow of the fluid at the fluid flow disrupter is disrupted
to create a pressure differential proximate the lower fluid output
port to draw the fluid into the lower fluid output port, and
further comprising a purging mechanism for purging air from the air
trap and preventing air from passing beyond the air trap.
2. The cartridge of claim 1 wherein the ratio of the height of the
fins to the width of the fins is from about 1:2 to 1:50.
3. The cartridge of claim 1 wherein the ratio of the height of the
fins to the width of the fins is from about 1:4 to 1:25.
4. The cartridge of claim 1 wherein the ratio of the height of the
fins to the width of the fins is from about 1:5 to 1:10.
5. The cartridge of claim 1 wherein the height of the fins ranges
from about 0.25 inches to about 1 inch.
6. The cartridge of claim 1 wherein the ratio of the flow path
depth to the height of the fins is from about 0.01:1 to 1:1.
7. The cartridge of claim 1 wherein the flow path of the heat
exchange zone has a depth of about 0.01 inches to about 0.25
inches.
8. The cartridge of claim 1 wherein the distance between a first
and second fin within the same plurality of fins is from about 0.25
inches to about 1 inch.
9. The cartridge of claim 1 wherein the heat exchanger is comprised
of two symmetric units fixed together.
10. The cartridge of claim 1 wherein the heat exchanger is
comprised of a single unit.
11. The cartridge of claim 1 wherein the heat exchanger is
comprised of at least two units fixed together.
12. The cartridge of claim 1 wherein the air-trap is
cylindrical.
13. The cartridge of claim 12 wherein the air-trap is taller than
it is wide.
14. The cartridge of claim 1 wherein the fluid flow disrupter
extends from an inner surface of the lower aspect of the
air-trap.
15. The cartridge of claim 1 wherein the purging mechanism utilizes
an ultrasonic detection mechanism to monitor fluid volume in the
air-trap.
16. The cartridge of claim 15 wherein the purging mechanism uses a
valve at a fluid output port and a valve at an air output port
working in tandem to force air out the air output port as the
volume of the fluid within the air-trap increases, to a
pre-determined level.
17. The cartridge of claim 1 wherein the air-trap can effectively
remove air when moved off vertical axis up to 45.degree..
18. The cartridge of claim 1 wherein the heat exchanger has a
surface of area exposed to a heating element is from about 30
square inches to 45 square inches.
19. The cartridge of claim 18 wherein the surface area is
substantially flat across said area.
20. A disposable infusion cartridge comprising: a. a heat exchanger
comprising an enclosed uniform tortious flow path containing short
segments of linear flow length, creating a ribbon of fluid, greater
in width than in segments of linear flow length, for enhanced
exposure to the inner surface of the heat exchanger; and b. a
cylindrical air-trap for removing air from the fluid comprising an
upper and lower aspect defining a longitudinal axis extending
centrally therebetween, and further comprising an upper fluid input
port, a lower fluid output port positioned off-center from the
longitudinal axis, an upper air output port, and a fluid flow
disrupter positioned off-center from the longitudinal axis and
proximate the lower fluid output port, wherein the air-trap creates
a vortex of fluid and the fluid flow disrupter disrupts the vortex
of fluid to create a pressure differential proximate the lower
fluid output port for drawing fluid into the lower fluid output
port.
21. The cartridge of claim 20 wherein the ratio of the length of
the short segments of the tortious flow path to the width of the
flow path is from about 1:2 to 1:50.
22. The cartridge of claim 20 wherein the ratio of the length of
the short segments of the tortious flow path to the width of the
flow path is from about 1:4 to 1:25.
23. The cartridge of claim 20 wherein the ratio of the length of
the short segments of the tortious flow path to the width of the
flow path is from about 1:5 to 1:10.
24. The cartridge of claim 20 wherein the length of the short
segments of the tortuous path are from about 0.25 inches to about 1
inch in length.
25. The cartridge of claim 20 wherein the depth of the tortious
flow path has a ratio of depth to length of the short segments from
about 0.01:1 to 1:1.
26. The cartridge of claim 20 wherein the tortious flow path of the
heat exchange zone has a depth of about 0.01 inches to about 0.25
inches.
27. The cartridge of claim 20 wherein the tortious flow path is
created via at least one plurality of fins.
28. The cartridge of claim 20 wherein the distance between a first
and second fin within a plurality of fins is from about 0.25 inches
to about 0.5 inches.
29. The cartridge of claim 20 wherein the fluid flow disrupter
extends from an inner surface of the air-trap.
30. The cartridge of claim 20 further comprising a purging
mechanism that utilizes an ultrasonic detection mechanism to
monitor fluid height.
31. The cartridge of claim 30 wherein the purging mechanism uses a
valve at the lower fluid output port and a valve at the upper air
output port working in tandem to force air out the upper air output
port as the volume of the fluid within the air-trap increases.
32. The cartridge of claim 31 wherein the valves of the purging
mechanism are controlled by monitoring mechanisms contained within
a pump housing reversibly attachable to the cartridge.
33. The cartridge of claim 20 wherein the air-trap can effectively
remove air when moved off vertical axis up to 45.degree..
34. The cartridge of claim 20 wherein the heat exchanger has a
surface of area exposed to a heating element is from about 30
square inches to about 45 square inches.
35. The cartridge of claim 20 wherein the surface area is
substantially flat across said area.
36. The cartridge of claim 20 further comprising at least one
pressure monitor for monitoring the pressure of fluid within the
disposable cartridge.
37. The cartridge of claim 20 further comprising at least one
bubble detector for monitoring the presence of a bubble within
fluid passing through the disposable cartridge.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to warming fluid for infusion to
a patient's body without damaging the fluid through exposure to
increased temperature as well as preventing the introduction of air
into the patient's body.
2. Background
Fluid required in treating a patient must often be stored in
comparatively cool to cold temperatures with respect to the
patient's body temperature. This often refrigerated storage is
necessary to preserve the fluids in a state so the function and
integrity of the fluid is maintained. Fluids such as blood and
other bodily fluids are typically stored at hypothermic
temperatures ranging from 2.degree. to 20.degree. Celsius.
Therefore, when introducing fluids into the patient's body it is
often necessary to heat the fluid to an appropriate temperature not
only to prevent any rapid decrease in the patient's body
temperature, but also to ensure that the fluid being introduced can
function as needed. It is known that the injection of cold fluids
into a patient's body can create a major source of conductive heat
loss within the patient, often placing the patient at further risk
by cooling, too quickly or, to a temperature where physiological
damage can occur.
In heating or warming the fluid, however, care must be taken to
ensure that the heating itself does not create a further
complication. For instance, if blood is exposed to a temperature of
above 45.degree. Celsius hemolysis, the destruction or severe
degradation, of the blood cells can occur. Likewise, if the fluid
is heated too high and then introduced into the patient's body,
physiological damage resulting from exposure to excessive
temperatures such as burns or other such scarring can occur.
Heating the fluid in bulk form usually requires the application of
too intense a heat source in order to heat the entire fluid with
any level of time efficiency. Likewise, heating the fluid over a
prolonged period of time can lead to increased exposure of the
material to the environment creating risks of contamination.
Getting the fluid into the patient requires adjustable flow so that
the proper amount of fluid depending upon the need is provided to
the patient. Combining the fluid delivery means with the proper and
efficient heating of the fluid is crucial to the proper delivery of
fluid to the patient. The prior art contains systems for warming
fluids as they are infused into a patient. The manner in which the
fluids are heated within these systems varies and can be
accomplished via convection or conduction. An example of a system
which poses clinical problems heats the fluid being delivered to
the patient via exposure to a heated fluid, such as water. Such
systems are usually cumbersome, require frequent cleaning, and can
pollute the clinical environment through the introduction of an
additional substance--the heating liquid. Such a system often
places a conduit through a liquid such as water, which is then
heated, and the fluid to be delivered to the patient is drawn
through the conduit thereby increasing the temperature of the fluid
to be delivered. Such a system can be deleterious to a sterile
environment and may not be properly transported. Furthermore, these
systems also have large mass which require significant power to
heat that mass yielding a significant time to achieve that
temperature, or achieve a stasis when a cold mass (like a bag of
chilled fluid) is introduced.
Moreover, during some fluid infusion procedures it is beneficial to
adjust the temperature of the patient's body either warmer or
cooler. As such it is extremely beneficial to have an adjustable
in-line fluid warming system so that the proper temperature can be
regulated. In instances of massive or emergent fluid loss, it is
often necessary to infuse extremely large amounts of fluid into the
patient's body. In such instances, traditional fluid heating
systems often place the fluid at risk by exposure to temperatures
which could damage the fluid because the fluid must be heated so
rapidly. Such problems remain largely unsolved by the art and need
for better in-line fluid infusers is abundant.
When introducing fluid into a patient's body it is crucial that air
not be introduced into the patient's body as well. Introduction of
air or air bubbles into a patient's body can cause extremely
deleterious effects. Air embolisms can occur if air accumulates in
a patient's blood stream resulting in cardiac arrhythmias, stroke,
or pulmonary infarct. Any of these potential infirmities can be
life threatening and need to be minimized in situations where high
volumes of bodily fluid are being infused. It is therefore
extremely important that during infusion of bodily fluid that both
the monitoring of air in the infusion system occurs to prevent
introduction into the patient's body.
Devices in the prior art seeking to warm fluid for infusion into
the body often suffer from very specific problems. For example, the
heater system described in U.S. Pat. No. 3,590,215 issued to
Anderson et al. uses regions of differing heat which the fluid
encounters as it progresses through the system. Specifically, the
heating element or elements described in Anderson et al. diminishes
the heat in the material warming the fluid from a hottest
temperature where the fluid enters the heat exchanger to a coolest
temperature where the fluid exits the heat exchanger. Such a
configuration not only makes it difficult to regulate the
temperature of the fluid as the flow rate changes, but it also runs
the risk of having to expose the fluid to temperatures above which
the fluid should be exposed to, running the risk of damaging the
fluid.
Likewise, the serpentine fluid flow path described in Anderson et
al. creates the typical laminar type flow seen in most heat
exchanger systems. For example, U.S. Pat. No. 5,245,693 to Ford et
al. describes a serpentine flow pattern which is long compared to
its width and wider compared to its depth. This type of flow is
consistent with a non-turbulent laminar type flow path. A
non-turbulent flow path requires additional heat energy to be
introduced into the fluid system in order to increase the
temperature of the fluid system uniformly to a desired
temperature.
SUMMARY OF THE INVENTION
The present invention is a system for increasing the temperature of
a fluid being infused into a patient's body while the infusion is
taking place. Such a heating system is also referred to as an
in-line heating infusion system. The present invention also
provides for improved monitoring of air in the infusion system such
to prevent the introduction of air into the patient's body
receiving the fluid infusion. The present invention also provides
for a system pump which provides a variable flow rate that serves a
vast amount of infusion needs and purposes.
A disposable cartridge in accordance with the present invention
will allow for the efficient transfer of heat energy to the fluid
being infused into the patient's body. The cartridge will further
ensure that deleterious amounts of air will not be introduced into
the patient's body.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevation view of the internal elements of a
disposable cartridge in accordance with the present invention.
FIG. 2a shows a different orientation of the disposable cartridge
in accordance with the present invention (near cover of disposable
removed).
FIG. 2b shows the side of the disposable cartridge of one
embodiment of the present invention which abuts the pump
housing.
FIG. 2c shows the pump housing with exposed platen embodying one
aspect of the present invention.
FIG. 3 shows one-half of the heat exchanger--one plurality of
fins.
FIG. 4 is a cross-section of the heat exchanger, artificially
hollowed, showing a fluid flow path in accordance with one
embodiment of the present invention.
FIG. 5 is an outside view of an air-trap in accordance with the
present invention.
FIG. 6 is a cross-section of an air-trap in accordance with the
present invention.
FIG. 7 shows the shape of fluid that would fill a heat exchanger in
accordance with the present invention.
FIG. 8 shows a disposable cartridge of one embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention contemplates a disposable heat exchange
cartridge for use in fluid infusion into a patient's body. The
disposable heat exchange cartridge is removably coupled to an
infusion pump device which provides not only the energy or power
required to covey heat to the fluid being infused, but also
provides the flow generating pump and mechanisms for monitoring and
regulating particular aspects of the fluid infusion system. In this
description of the invention reference will be made to the
embodiments shown in FIGS. 1-8 wherein like numerals are used to
designate like parts throughout. FIGS. 1 and 2a-c describe a
currently preferred embodiment of the present invention and should
not be viewed as limiting.
One embodiment of the present invention is a disposable fluid
infusion cartridge comprising a heat exchanger having upper and
lower aspects and an internal heat exchange zone defined by a first
and second plurality of overlapping fins, creating a substantially
uniform flow path depth, wherein each fin has a ratio of height to
width of at least 1:2, whereby fluid enters the lower aspect of the
heat exchanger via a lower port and fills a lower flow cavity
across the width of the heat exchange zone prior to flowing through
the heat exchange zone and out an upper port at the upper aspect of
the heat exchanger.
The disposable fluid infusion cartridge can further comprise an
air-trap having upper and lower aspects, an inner surface, which
receives the fluid from the heat exchanger, and further comprising
a fluid flow disrupter and a purging mechanism for purging air from
the air trap and preventing air from passing beyond the air trap.
The disposable cartridge of this embodiment can have a ratio of the
height of the fins to the width of the fins from about 1:2 to 1:50,
preferably from about 1:4 to 1:25, and most preferably from about
1:5 to 1:10. The height of the fins in the present embodiment can
be from about 0.25 inches to about 1 inch.
The disposable cartridge of the present embodiment can have a ratio
of the flow path depth to the height of the fins from about 0.01:1
to about 1:1. The flow path of the heat exchange zone of the
present embodiment can have a depth of about 0.01 inches to about
0.25 inches. Moreover, the distance between a first and second fin
within the same plurality of fins can be from about 0.25 inches to
about 0.5 inches. Also, the heat exchanger of the present invention
can be comprised of two symmetric units fixed together, a single
unit, or comprised of at least two units fixed together.
The air-trap of the present embodiment of a disposable fluid
infusion system can be cylindrical wherein the air-trap is taller
than it is wide. The air-trap of the present embodiment further
comprises a fluid flow disrupter which extends from the inner
surface of the lower aspect of the air-trap. Moreover, the purging
mechanism can utilize an ultrasonic detection mechanism to monitor
fluid volume in the air-trap. Likewise, the purging mechanism of
the present embodiment can utilize a valve at a fluid output port
and a valve at an air output port working in tandem to force air
out the air output port as the volume of the fluid within the
air-trap increases to a pre-determined level. The air-trap of the
present embodiment can effectively remove air when moved off its
vertical axis up to 45.degree..
In another embodiment of the present invention the disposable
infusion cartridge can comprise a heat exchanger comprising an
enclosed uniform tortious flow path containing short segments of
linear flow length, creating a ribbon of fluid, greater in width
than the length of segments of linear flow length, for enhanced
exposure to the inner surface of the heat exchanger and mixing of
the fluid via non-laminar flow to enhance heat transfer within the
fluid.
The disposable infusion cartridge of this embodiment can further
comprise a cylindrical air-trap for removing air from the
disposable cartridge comprising an upper and lower aspect and
further comprising a fluid input port, a fluid output port, an air
output port, and a fluid flow disrupter wherein the air-trap
creates a vortex of fluid and the fluid flow disrupter creates a
pressure differential at the fluid output port for drawing fluid
out of the air-trap.
The cartridge of this embodiment can posses a ratio of the length
of the short segments of the tortious flow path to the width of the
flow path from about 1:2 to 1:50, preferably from about 1:4 to
1:25, and most preferably from about 1:5 to 1:10. In this
embodiment, the length of the short segments of the tortious path
can be from about 0.25 inches to about 1 inch in length. Likewise,
the depth of the tortious flow path has a ratio of depth to length
of the short segments of flow length from about 0.01:1 to 1:1, with
specific depth of about 0.01 inches to about 0.25 inches.
The heat exchanger of the present invention can create the tortious
path via at least one plurality of fins. Within that plurality of
fins, the distance between a first and second fin can be from about
0.25 inches to about 0.5 inches.
The fluid-flow disrupter of the air-trap of the current embodiment
can extend from the inner surface of the air-trap. Moreover, the
purging mechanism may utilize an ultrasonic detection mechanism to
monitor fluid height. Likewise, the purging mechanism may use a
valve at a fluid output port and a valve at an air output port
working in tandem to force air out the air output port as the
volume of the fluid within the air-trap increases. Also, the valves
of the purging mechanism can be controlled by monitoring mechanisms
contained within a pump housing reversibly attachable to the
cartridge.
In an additional embodiment of the present infusion cartridge, the
device may comprise at least one pressure monitor for monitoring
the pressure of fluid within the disposable cartridge as well as a
bubble detector for monitoring the presence of bubbles within fluid
passing through the disposable cartridge.
The heat exchanger 101, as depicted in FIG. 1, is contained within
the disposable cartridge 100. The disposable cartridge is removably
attached to the pump system such that once the treatment is
completed, the disposable cartridge can be removed and discarded.
The disposable cartridge is self-contained and once attached to the
pump system need not be adjusted or manipulated. Fluid enters the
disposable cartridge in the primary in-flow tube 102 which draws
fluid from the fluid source. The fluid is drawn into the primary
in-flow tube 102 and proceeds past a first t-junction which serves
as the inflow pressure monitor 103. The inflow pressure monitor 103
is in fluid communication with a first air chamber 151. The inflow
pressure monitor 103 determines the pressure of the fluid flow as
it enters the pump loop 104 to allow for proper regulation of the
fluid flow. The pump loop 104 interacts with a rolling or otherwise
detachable pumping system. The pump loop 104 when interacting with
a pumping system pushes the fluid through the disposable cartridge
100. When the fluid leaves the pump loop 104 it flows through a
second t-junction which serves as the outflow pressure monitor 105.
The outflow pressure monitor 105 determines the pressure of the
fluid as it exits the pump loop 104 so that the flow of the fluid
through the disposable cartridge 100 can be regulated.
The fluid then passes into the heat exchanger 101 via the exchanger
inlet port 106 at the lower aspect of the heat exchanger. After the
fluid passes through the turbulent environment established by the
heat exchanger 101 it exits via the exchanger outlet port 107
located a position opposite the exchanger inlet port 106 at the
upper aspect of the heat exchanger 101. At this point, the fluid
for infusion has undergone its warming and the desired temperature
has been reached.
The fluid exits the heat exchanger 101 via the exchanger outlet
port 107 and then enters the air-trap 110 at about the mid-point
along the long-axis of the air-trap 110. Fluid flows out of the
air-trap 110 and through a third t-junction which serves as the
out-flow bubble detector 112. The out-flow bubble detector 112
determines whether excess amounts of air have infiltrated the
system. If an unacceptable level of air remains in the fluid as it
flows past the out-flow bubble detector 112, the system will not
allow the infusion of that fluid into the patient's body. If the
fluid contains no air, or a minimal amount of air such to be
acceptable, the fluid passes the out-flow bubble detector and into
the patient via the primary out-flow tube 111.
A detailed description of the heat exchanger 101 requires reference
to FIGS. 3 and 4. Heat exchanger 101 can be created by two halves
cast from the same mold each containing a plurality of fins. A
first halve 301 is comprised of the exchanger inlet port 106 and a
plurality of fins comprising a series of spaced fins 302. With the
exception of a specially sized flow fin 303, each of the fins 302
are of equal size and are spaced equidistant from one another. As
fluid enters the heat exchanger 101 through the exchanger inlet
port 106, the fluid fills the flow cavity 304 defined by the inner
walls of the heat exchanger and the flow fin 303. When in
operation, the heat exchanger is oriented such that a lower aspect,
where the inlet port is located, and an upper aspect, where the
outlet port is located, are oriented in a vertical form forcing
fluid to flow in an upwardly direction through the heat exchanger
and against gravitational forces. Because of the special shape
given the flow fin 303 the fluid fills the flow cavity 304 before
proceeding up through the heat exchanger 101.
Using FIG. 4 to describe the flow of fluid through the heat
exchanger 101, fluid enters the flow cavity 304 via the exchanger
inlet port. Because of the differentially sized flow fin 303, fluid
first fills the flow cavity 304 before rising over the first fin.
This preliminary filling allows the fluid to fill the width of the
heat exchanger and flow as a wide ribbon of fluid across the
fins--opposed to a laminar flow through a long but narrow conduit.
The flow fin 303 accomplishes the appropriate spreading of fluid by
creating a thinner flow gap 305 between the flow fin 303 and the
first of the plurality of fins of regular shape. The fluid then
flows up the length of the heat exchanger 101 between the exchanger
inlet port and the exchanger outlet port. As the fluid rises, it
travels in wave form as a shallow but wide ribbon of fluid. The
wide-flow, short linear track flow pattern created by the heat
exchanger creates a turbulent flow causing increased molecular
circulation within the fluid. While laminar flow within typical
conduits, such as tubes, see higher molecular "turnover" in the
central portion of the conduit, the turbulent flow within the heat
exchanger 101 provides much more exposure of different molecules to
the interior surface of the heat exchanger thereby facilitating
more efficient and effective energy transfer.
Returning to FIG. 3, the other halve of the heat exchanger can be
created from the same mold, wherein the exchanger inlet port 106,
becomes the exchanger outlet port. Once formed, the two halves are
mounted together using means known in the art, including but not
limited to bolts, screws, or other mechanical means, as well as
glues, cements, or other chemical means. If mechanical means are
used, then fixation tabs 306 can be used to house the fixation
devices.
FIG. 4, the cross-section view of the heat exchanger, further shows
the seal seat 401 which provides for a space to place a seal about
the circumference of the heat exchanger to increase the liquid
impermeability of the heat exchanger, such as an o-ring. It should
be noted that while the heat exchanger of the present embodiment is
described as being formed from two identical halves the heat
exchanger could be formed as a singular piece or more than two
pieces. For ease in manufacture, however, two identical halves as
described herein allows for the proper result through less
cost.
The heat exchanger of the present invention can be formed from any
number of materials: cast anodized aluminum, copper, gold, and the
like. The material chosen for use in the heat exchanger of the
present invention must be capable of adequate heat conduction and
dispersion to ensure proper heat distribution across the surface as
well as heat transfer to the fluid desired to be warmed.
Thermodynamics dictates that for two materials with the same
specific heat, that is the amount of heat energy required to change
the temperature of the material one unit per unit of mass, the
material with a greater mass will more efficiently transfer heat to
the material with a lesser mass. This efficiency level is often
understood as thermal capacitance--in that materials with greater
thermal capacitance (i.e. mass) will retain more heat while
transferring energy to the adjacent material sufficient to greatly
increase the temperature of the second material without the
unwanted loss of energy. Analogizing the heat exchange occurring
between the heat exchanger and the infusion fluid by way of
example, a material with a mass of 1.5 kg is heated to 60.degree.
C. and placed in close, direct contact with a material having a
mass of 0.5 kg at a temperature of 40.degree. C. When the heating
is complete, both materials will achieve a temperature of
55.degree. C. The energy stored by the hotter component via its
increased mass allows for a better exchange of heat energy between
the two materials. The selection of a material, given the special
requirements of the present invention, therefore requires the
consideration of the mass of the material as well as the
thermodynamic properties of that material.
FIG. 5 shows an enlarged view of the air-trap 110 and its
connective conduits. While the air-trap is described with reference
to specific shapes, it should apparent to one of skill in the art
that any shape which would allow for the reversal of fluid flow
direction at the fluid output port of the air-trap will allow for
the monitoring and removal of air from the cartridge system. The
air-trap is generally cylindrical in shape with a domed top 501 and
flattened bottom 502. Fluid enters the air-trap 110 at the air-trap
intake port 503 located at approximately midway along the long axis
of the air-trap. Fluid enters the air-trap 110 from the heat
exchanger in order to remove any air trapped or introduced into the
fluid. The air to be removed may have come from failure to purge
the fluid source of air before introducing it to the present
invention. It is also possible that the heating of the fluid causes
the release of bound gas creating bubbles which if allowed to enter
the patient's body could be deleterious or even deadly. Fluid exits
the air-trap 110 through the fluid output port 505 located at the
bottom 502 of the air-trap.
FIG. 6 depicts a cross-section of the air-trap 110. In this view,
one can see the air-trap intake port 503 as it interfaces with the
air-trap. The air-trap intake port 503 is smoothed to the inside
wall of the air-trap and is positioned off of the mid-line of the
long axis of the air-trap. This position of the air-trap intake
port 503 relative to the mid-line of the long axis of the air-trap
causes the fluid being introduced to the air-trap to flow about the
cylindrical form of the air-trap in a clockwise direction as the
fluid fills and continues to enter the air-trap. This flow pattern
creates a vortex within the air-trap pulling air downward toward
the fluid output port. At the bottom 502 of the air-trap there is
located a flow disrupter 601 which is positioned adjacent to the
fluid output port 505. The flow disrupter can extend from the inner
wall of the air-trap or the inner wall of the bottom 502 of the
air-trap. As the fluid, which is traveling clockwise about the
air-trap, flows across the flow disrupter 601, a differential in
pressure at the fluid output port 505 is created drawing the liquid
out of the air-trap and allowing the air or gas bubbles to flow
upward along the long-axis of the air-trap.
Returning to FIG. 5, the level of fluid within the air-trap is
continuously monitored while the infusion device is being operated.
When the level of fluid in the air-trap 110 drops below the lower
level sensor 506 a valve located at or about the fluid output port
505 closes. At approximately the same time that the valve located
at or about the fluid output port 505 closes, a valve located at or
about the air output port 504 opens. With the fluid output port 505
closed, fluid entering the air-trap 110 forces any air present in
the air-trap up the long axis of the air-trap. Because the air
output port 504 is open, any air within the air-trap is forced out
of the air-trap and into the air output tube 108 shown in FIG. 1.
When the level of fluid in the air-trap 110 rises above the upper
level sensor 507, the valve at the air output port 504 closes. At
approximately the same time that the valve at the air output port
504 closes, the valve at the fluid output port 505 opens again.
With the fluid output port 505 open, fluid flow out to the patient
via the primary out-flow tube 111 is restored.
The air-trap embodied by the present invention is capable of
functioning at varying inclinations and orientations. The cylinder
formed by the air-trap is between 3 inches and 10 inches in height,
preferably between 3.5 inches and 7 inches, and most preferably
between 4 inches and 6 inches. The diameter of the air-trap
cylinder is between 0.5 inches and 2 inches, preferably 0.625
inches and 1.5 inches, and most preferably 0.75 inches and 1.25
inches. The air-trap is able to properly remove air from the fluid
as it passes through even when the air-trap is tilted off its
vertical axis up to 45.degree..
As discussed above, efficient transfer of heat from the heating
element to the fluid to be warmed heavily impacts the present
invention. The present invention's use of a wide flow, short linear
travel flow pattern allows for a more turbulent flow with an
extremely large contact area. The contact area being described is
the area of interface between the heat exchanger and the fluid
passing through. Described as a ribbon of fluid, the fluid
traveling through a heat exchanger made in accordance with the
present invention will flow in very short linear distances along
the short segments of linear distance but will instead be
proportionately wider. In fact, the cavity created for fluid flow
through the heat exchanger is wider than it is long, and longer
than it is deep thereby creating a tortious ribbon shape for the
fluid to pass through. FIG. 7 is a representation of the fluid
flowing through the heat exchanger 100. The fluid flow of FIG. 7
first is shown as having filled the exchanger inlet port as the
inlet fluid 701. The fluid then fills the flow cavity as cavity
fluid 702. The fluid then flows up the heat exchanger first through
the smaller gap created by the flow fin indicated as the first
restricted flow 703. It should be noted that linear flow distance
.lamda., defined by the height of the fins and representing the
short segments of flow length, is less than the flow width .omega..
The ratio between the linear flow distance .lamda. and the flow
width .omega. can be from about 1:2 to 1:50, preferably from 1:4 to
1:25, and most preferably from 1:5 to 1:10. It is the ratio between
the linear flow distance and the flow width which creates the
ribbon-like flow pattern depicted in FIG. 7. By having such a short
linear flow, the fluid flows through the heat exchanger with more
turbulence than a typical long linear flow serpentine path. The
introduction of turbulence in the fluid avoids the laminar type
flow that such a serpentine flow path may create. As opposed to
merely the molecules within the central portion of the fluid flow,
that is those molecules not located directed at the interface,
changing over faster than the molecules at the interface, the
turbulent flow created by the present invention exposes more fluid
molecules to the interface which allows for an enhanced heat
transfer. Likewise, this turbulent flow creates more contact
between the molecules within the fluid flowing through the heat
exchanger. With more contact between the molecules within the
fluid, more heat exchange and transfer can occur driving the
efficient exchange of heat from the exchanger to the fluid to be
delivered to the patient.
A heat exchanger made in accordance with the present invention
creates this turbulent flow path and maintains it as the fluid
flows over the fins. The fins, as depicted in FIG. 3, create
one-half of the flow path for the fluid to follow. The fins on the
same side of the heat exchanger are evenly sized and spaced, that
is the distance between a first fin 307 and a second fin 308 is the
same across to overall span of the heat exchanger. For the purposes
of heat transfer involving a fluid flowing in the heat exchanger,
the distance between a first and second fin of the same plurality
of fins can be from 0.25 inches to 0.5 inches, preferably from 0.35
inches to 0.45 inches, and most preferably from 0.37 inches to 0.43
inches. The length of the fins on one-half of the heat exchanger
dictates the linear flow distance. The length of the fins can be
from about 0.25 inches to 1.0 inches, preferably from 0.5 inches to
0.8 inches, and most preferably from 0.6 inches to 0.7 inches. The
flow path also contains a depth element created by the separation
distance between the top of the fins in a first plurality of fins
and the valley between two fins in a second plurality of fins. The
flow path can have a depth of about 0.01 inches to 0.25 inches,
preferably 0.03 inches to 0.125 inches, and most preferably 0.04
inches to 0.110 inches. The width of fins can be from 3 inches to 6
inches, preferably 3.5 inches to 5 inches, and most preferably 4
inches to 4.5 inches.
Transfer of heat energy to the heat exchanger occurs at the exposed
portion of the heat exchanger, that is the portion not covered or
contained within the disposable cartridge. The flat plate 801 of
the heat exchanger is visible in FIG. 8 exposed from the housing
802 of the disposable cartridge 100. The disposable cartridge 100
is removably fixed to the pump system via a first attachment region
803 and a second attachment region 804. The attachment regions
allow the disposable cartridge to be affixed to the pump system
securely and tightly. It is extremely important that the flat plate
801 of the heat exchanger be located as close to the heating
element or platen as possible. It is equally important and
difficult to ensure that the flat plate 801 of the heat exchanger
is uniformly close to the heating element or platen. Even known
smooth materials, when dealing with solids, are rarely completely
in contact when considered at a microscopic level. Therefore, flat
plate 801 should be as reasonably uniform and smooth as possible in
order to achieve as much surface area contacting the heating
element or platen. The surface area of the flat plate 801 which
contacts the heating element or platen can be from about 20 square
inches to about 100 square inches, preferably from about 25 square
inches to about 50 square inches, and most preferably from about 30
square inches to about 45 square inches. Likewise, the pressure
exerted onto the disposable cartridge 100 to hold the flat plate
801 in close contact with the heating element or platen must
increase if the surface of the flat plate 801 and the heating
element or platen are not smooth. If the flat plate 801 and the
heating element or platen are positioned immediately next to one
another, it is considered that an air interface exists between the
two surfaces. Because while the surfaces will be extremely close
and pressure will be exerted on the flat plate 801 such to press
the two surfaces together, gaps between the surfaces will remain.
It is therefore possible to reduce these gaps by coating the
heating element or platen which contacts the flat plate 801 of the
heat exchanger with a thermal pad which conforms and fills the
voids between the surfaces with a material that is a better heat
conductor than air yet allowing a reasonable contact pressure to be
used. If air serves as the interface between the surface of the
flat plate 801 of the heat exchanger and the heating element or
platen, then greater pressure must be exerted on the system in
order to achieve an efficient transfer of heat energy. Using a
material which fills the gaps and is a better heat conductor than
air allows the system to be established with a lesser and more
reasonable pressure applied to the surface interface.
EXAMPLE
An infusion system under the present invention in shown in FIG.
2a-c. The disposable cartridge is shown with half of its outer
cover removed in FIG. 2a. For orientation purposes, the air-trap
110 is visible extending out of the outer cover 201 at the
right-hand portion of the figure. The outer cover of the disposable
is made of sturdy polymeric material. FIG. 2b shows the side of the
disposable cartridge which will contact the pump housing 250 shown
in FIG. 2c. Again for orientation, the air-trap 110 is shown in
FIG. 2b at the left-hand portion of the figure extending out from
the outer cover 201. The exposure surface 225 of the heat exchanger
101, which will be in contact with the platen of the pump system,
is shown in FIG. 2b. FIG. 2c shows the pump housing which contains
the roller pump to interact with the pump loop 104. FIG. 2c also
shows the platen 275 which provides the heat energy to the heat
exchanger contained within the disposable cartridge. All elements
of this Example are in fluid connection with one another.
Engaging handle 280 allows the user to reversibly attach the
disposable 100 to the pump housing 250 by clamping or other locking
mechanisms that extend from lock housings 285 located about the
platen 275. When engaging handle 280 is manipulated, the clamping
or other locking mechanisms contained within the lock housings 285
extend and engage the disposable 100 at attachment points 210
located about the exposure surface 225 of the heat exchanger 101.
When engaged, the force provided to couple the exposure surface 225
of the heat exchanger 101 to the platen 275 is from about 170
pounds to 230 pounds with the normal force being about 200 pounds.
Located between the exposure surface 225 and the platen 275 is a
conductive material, or silpad, which allows for extremely close
and uniform contact between the platen and the heat exchanger. The
material chosen as the silpad is a silicone-based pad, Chomerics
T500.RTM., supplied by Chomerics, located in Woburn, Mass. The
silpad allows for better heat transfer from the platen 275 to the
heat exchanger 101 than an interface of air would allow. In this
Example, the silpad is about 0.02 inches thick, give or take 0.005
inches, and covers the entire platen. Moreover, in this Example the
surface area of the flat plate 801 which contacts the heating
element or platen is about 35 square inches.
For the purposes of this Example, the fluid being infused into the
patient is blood. The fluid entering the pump system embodied in
this Example is 20.degree. C. The rate at which infusion is
conducted is 1000 ml/min. The pump contained within the pump
housing in this Example is capable of pumping fluid at a rate of 10
ml/hr to 1200 ml/min.
Once the cartridge is engaged, the rolling pump contained within
the pump housing will apply pumping pressure to the pump loop 104
causing fluid to flow from a fluid source through the cartridge
sufficient to infuse at 1000 ml/min. Again referring to FIG. 1, the
blood is drawn into the primary in-flow tube 102 and proceeds past
a first t-junction which serves as the inflow pressure monitor 103.
The inflow pressure monitor 103 is in fluid communication with a
first air chamber 151. The inflow pressure monitor 103 determines
the pressure of the blood flow as it enters the pump loop 104 to
allow for proper regulation of the blood flow.
The inflow pressure monitor 103 monitors negative pressure in the
event that fluid remains within the disposable cartridge but is not
flowing in the direction of the patient. Such a circumstance could
arise if the fluid source bag collapses yet fluid remains in the
cartridge. If the pressure at the inflow pressure monitor 103 falls
below 1 mmHg, then the pump will stop pumping.
When the blood leaves the pump loop 104 it flows through a second
t-junction which serves as the outflow pressure monitor 105. The
outflow pressure monitor 105 determines the pressure of the blood
as it exits the pump loop 104 so that the flow of the blood through
the disposable cartridge 100 can be regulated. The outflow pressure
monitor measures the pressure of the fluid proceeding through the
cartridge. Here the pressure monitors for flow blockage so that
when the pressure exceeds 500 mmHg the pump will shut down to avoid
damage.
The blood then passes into the heat exchanger 101 via the exchanger
inlet port 106. The heat exchanger 101 of this Example is created
from two halves as depicted in FIG. 3. The two halves are created
from the same mold such that inverting one mold and fixing the two
together creates the heat exchanger. The material used in the
creation of the heat exchanger of this Example was anodized
aluminum. The use of this material accomplishes the goal of the
present invention by creating a large mass differential between the
heat exchanger and the fluid, blood, to be warmed. The heat
conduction ability of the anodized aluminum allows for excellent
dissipation of heat energy across the heat exchanger. The anodized
surface of the aluminum creates a biological inert surface such to
prevent either the reaction with, or adsorption of, biological
material while the blood or other fluid passes across it. In the
present Example, dealing with blood, protein adsorption to the
surface of the material may generate a trigger to the clotting
cascade. The adsorbed proteins to the inner surface of the heat
exchanger, even if they do not trigger the clotting cascade, can
become degraded and detach. Once detached from the surface of the
heat exchanger, these degraded or denatured proteins may react with
other proteins or the cells contained within the blood in
deleterious manners. The anodized inner surface of the heat
exchanger thus prevents damage from occurring to the blood as it
passes through the heat exchanger.
When a cartridge according to the present invention is used, the
effective exchange of heat from the heat exchanger to the fluid
being infused achieve the appropriate rise in temperature of the
fluid without having to expose the fluid to a temperature of
45.degree. C. or greater. Instead of having regions of varied
temperature to which the blood or fluid is exposed, the heat
exchanger's constant temperature allows for more efficient transfer
of heat energy to the blood. At a flow rate of 1000 ml/min,
achieving a fluid exit temperature of 37.degree. C. means never
having to expose the blood to a temperature of 45.degree. C. which
could be deleterious to the fluid being infused. In fact, using
anodized aluminum yielded a 95-96% efficiency in transferring heat
energy to blood sufficient to generate a 17.degree. C. rise in
temperature.
Once the blood enters the heat exchanger, the blood fills the flow
cavity before proceeding to traverse the entirety of the heat
exchanger. The blood fills the flow cavity first because of the
narrower flow area created by the flow fin which defines the flow
cavity. By creating a smaller flow path to flow over the first fin,
as depicted in FIG. 7, the blood will not traverse the long axis of
the heat exchanger before it fills the flow cavity causing the flow
pattern across the heat exchanger's fins to be a wide ribbon-like
shape.
The fins used in the heat exchanger described in FIGS. 2a-c are
spaced at about 0.4 inches apart. The depth of the flow path
created by the separation of the two pluralities of fins is about
0.08 inches. The fins are about 4.3 inches wide and 0.62 inches in
height. This creates a ratio of linear flow distance to width of
about 1:7. The flow fin 303, as seen in FIG. 3, is wider than the
remainder of fins across the heat exchanger. That increased width
of the flow fin 303 creates a narrower flow path at that fin when
the two halves of the heat exchanger are connected. In this
Example, the width of the flow path created by the flow fin 303 is
about 0.03 inches. Given that the blood flowing through the heat
exchanger in this Example will travel along a path of least
resistance, the flow cavity 304 will fill before the blood travels
past the flow fin 303. The blood then travels over the fins which
creates a turbulent flow pattern for the blood as it travels
through the heat exchanger. This turbulent flow ensures an
increased exposure of more molecules within the blood fluid to the
heat exchanger thereby increasing the efficient transfer of heat
energy.
Once the blood flow reaches the top of the heat exchanger it exits
the via the exchanger outlet port 107 located a position opposite
the exchanger inlet port 106 of the heat exchanger 101. At this
point, the fluid for infusion has undergone its warming and the
desired temperature has been reached. The blood then enters the
air-trap 110 at a location approximately midway between the top and
bottom of the long-axis of the air-trap 110. In this Example, the
air-trap is about 4.2 inches along its long, vertical axis and
about 1 inch in diameter. The air-trap intake port 503 is located
about 2.1 inches from the bottom of the air-trap (see FIG. 6). As
the blood passes through the air-trap intake port, the blood
travels in a clockwise direction as the blood fills the air-trap.
This clockwise flow of blood creates a vortex of fluid in the
air-trap. The fluid flow disrupter 601, which in this example
extends from the interior surface of the bottom of the air-trap up
about 0.5 inches, creates a sufficient pressure differential at the
fluid output port 505 to draw the blood out and not any trapped
air.
Air may become trapped in the blood in this Example via several
mechanisms. Through spiking the blood as it is attached to the pump
system for infusion, in essence failing to properly purge the
source of the blood before attachment to the system. Also, the
heating of the fluid itself can cause the release of stored gas
within the blood which may be deleterious if introduced into the
patient.
As the amount of air in the air-trap 110 increases, the level of
blood in this Example lowers within the air-trap. When the blood is
below the lower level sensor 506, which in this Example is an
ultrasonic sensor, the valve at the fluid output port 505 closes.
When the valve at the fluid output port 505 is closed, the valve at
the air output port 504 located at the top of the air-trap is open.
This increases the blood volume in the air-trap forcing air out of
the air output port 504. The ultrasonic sensors are located in the
pump housing 250. The ultrasonic sensors utilize silicon buttons
attached to the air-trap at the lower level sensor 506 and upper
level sensor 507 in order to effectively monitor the level of fluid
within the air-trap. When the level of blood rises above the upper
level sensor 507, also an ultrasonic sensor, the valve at the air
output port 504 closes. At approximately the same time that the
valve at the air output port closes, the valve at the fluid output
port 505 opens and blood exits the air-trap and proceeds toward the
patient.
In this Example, the fluid then passes through a third pressure
monitor which controls the overall flow within the cartridge based
on pressure. If there is blockage, and the pressure begins to rise,
this pressure monitor will try to keep the pressure within an
acceptable range which can be between 100 and 300 mmHg. If the
pressure at this pressure monitors rises above 500 mmHg the pump
will shut down.
In the present Example, however, before blood reaches the patient
it passes through the out-flow bubble detector 112 (see FIG. 1).
The out-flow bubble detector analyzes the blood on its way to the
patient to determine that the air-trap removed potentially
deleterious air from the system. The bubble detector to this
Example uses an ultrasonic sensor which sends a signal across the
tube. Any air bubbles present in the system will attenuate the
signal. The system will shut the pump down if bubbles as small as
30 to 50 .mu.L are detected. The system is able to detect bubbles
of this size at the maximum flow rate of 1200 ml/min.
* * * * *